Determinants of CD8+ T cell Aging and Reduced Function in B cell Cancer Summary Chimeric antigen receptor (CAR)-engineered T cells provide a breakthrough for personalized cancer therapy. In this strategy, a patient's own T cells are genetically reprogrammed to recognize and kill antigen-expressing tumor cells. Robust clinical responses are seen with CAR T therapy of acute lymphocytic leukemia (ALL) in children and young adults, but only a small subset of individuals with advanced-age B cell cancers such as multiple myeloma (MM) and chronic lymphocytic leukemia (CLL) experience remission. These malignancies represent a challenge in that initial generation of CAR T cells is not possible in many elderly patients due to poor proliferative capacity in association with accelerated aging phenotypes and transcriptomic signatures enriched in genes that drive senescence and cell cycle arrest, as indicated by our preliminary data. Furthermore, in vivo expansion of CAR T cells in these individuals is modest, which may be attributed to senescent proliferative arrest and premature loss of early memory T cells. Our previous studies have indicated that in CLL, durable remission was associated with higher peak CAR T cell replicative capacity, greater long-term persistence, and modulation of specific T cell pathways. For example, disruption of TET2, which encodes an enzyme involved in CpG demethylation, was associated with a notable T cell expansion in a CLL patient undergoing successful therapy, thus marking an epigenetic pathway for future modulation to improve therapeutic efficacy. Because a significant portion of the aging population of MM and CLL patients does not experience therapeutic levels of CAR T cell expansion and anti-tumor activity, it is important to investigate factors leading to accelerated aging of CD8+ T cells in the setting of these malignancies. In the course of other studies we have devised a series of methods to systematically determine how MM and CLL may contribute to the process of CD8+ T cell aging. We thus propose the following Specific Aims: Aim 1. We will examine the impact of MM and CLL on immune aging as it relates to CD8+ T cell differentiation state, telomere length, p16INK4A levels, and T cell receptor (TCR) repertoire diversity in MM and CLL patients relative to age-matched healthy controls. Aim 2. We will characterize the epigenetic and transcriptional landscapes of major CD8+ T cell subsets in MM and CLL patients compared to age/gender-matched healthy subjects and explore the influence of disease on underlying networks that regulate immunosenescence. Aim 3. We will determine if strategies that may restore the normal replicative lifespan of CD8+ T cells such as enhancing telomerase, inhibiting TET2 and/or modulating the pathways identified in Aim 2 translate into improved anti-tumor function. These studies will allow us to gain a deeper understanding of how these cancers affect CD8+ T cell aging to bring about dysfunction through epigenetic regulation of gene expression. Intersecting this information with immunological aging status will make possible development of methods to modulate the cellular pathways involved in CAR T cell anti-tumor potency with the goal of improving clinical outcomes.